Magnesium and its alloys are recognized as having the lowest density of the structural metals. As such, they are used in many devices where low weight structural materials are valued. However, the cost of magnesium alloys is relatively high, and that limits their usage. The cost of magnesium is high as compared to that of aluminum despite the that there are several producers of magnesium metal, and the practices by which it is manufactured are of sufficient age that they have been subject to continuous improvements. Further, there are large resources of magnesium in sea water, brines, lakes and minerals such as magnesite, dolomite, etc.
In general, magnesium is produced by two processes: (1) magnesium chloride electrolysis and (2) thermal magnesium oxide reduction. The electrolysis process produces 3/4 of the world's magnesium at a lower cost than the thermal process. There are similarities between the electrolytic processes which differ mainly in the preparation of magnesium chloride feed. Much of the cost of producing magnesium results from the preparation of magnesium chloride suitable for electrolytic reduction. This stems from the requirement of providing the magnesium chloride in a form free of magnesium oxide or in a sufficiently dehydrated form that magnesium oxide formation in the electrolyte is minimized or avoided. The presence of undissolved magnesium oxide in the present electrolyte compositions leads to the formation of magnesium-containing sludge which results in losses of magnesium and reduces process efficiencies.
There remains a substantial need for magnesium production processes that can utilize magnesium oxide or partially dehydrated magnesium chloride as a feed material without forming magnesium oxide from the hydrated feedstock.